Apparatus for the production of music



Dec. 17, 1940. B. F. MIESSNER 2,225,195

APPARATUS FOR THE PRODUCTION OP MUSIC Filed Sept. 13, 1958 IN VEN TOR:

Patented Dec. 17, 1940 UNITED STATES APPARATUS FOR THE PRODUCTION OFMUSIC BenJamin F. Miessncr, Millburn Township, Essex County, N. J.,assignor to Miessner Inventions, 1110., Township of Mlllburn, N. 1., acorporation of New Jersey Application September 13, 1938, Serial No.229,650

17 Claims.

This invention relates to the production of music, and more particularlyto that production involving the mechanico-electro-acoustic translationof the vibrations of tuned vibrators. While not in all its aspectsnecessarily limited therechanico-electro-acoustlc translation dispenseswith, or at least renders secondary, the requirement for a resonator (e.g., a soundboard) to effect direct mechanico-acoustic translation fromthe vibrators. But, over and above that direct translation from thevibrators, the resonator of conventional instruments has performedadditional functions of considerable importance in determining thecharacteristics of the output tones. One of these functions is thevibrational intercoupllng of the vibrators; and it has been pointed outthat, even though the resonator is to be eliminated or reduced in itsradiating or translational effectiveness, intervibrator coupling mayvery advantageously be retained. An object of the instant invention isto provide a novel and improved means for coupling the vibratorstogether in instruments of the class described.

In stringed instruments the resonator is conventionally a vibratilesupport on which the strings bear, for example through a bridge. It isan object of the invention to provide a vibratile string support ofparticularly simple nature and of small radiating propensity.

Another important function of the resonato of conventional instrumentshas been to influence the vibrational modes of the vibrators and theamplitudes of their vibrations, by vibratory reaction between vibratorand resonator. Itis an object of my invention to provide an. improvedvibrator-coupling or -supporting means which carries out this influence.

The nature of this influence'depends on the predominant naturalfrequencies of vibration of the resonator in its several portionsrespectively most closely associated with the several strings v or othervibrators. It is an object of this invention to relate the naturalfrequencies of the several portions of the vibrator-supporting orconpling means to each other, and to the vibrator frequencies, in anovelmanner. for the production of improved output tones throughout a widepitch range.

While the vibrator-supporting or -coupling' means according to myinvention preferably has small sound-collecting propensities, yet undersome circumstances with the output loudspeaker of the instrument nearthe vibrators there may still occur acoustic or conductive feed-backfrom the loudspeaker, which may have the effect of producing sustainedoscillations or at least distortion. It is an object of my invention toprovide improved means for neutralizing, or suppressing the effect of,this feed-back.

Other and allied objects will more fully appear 10 from the followingdescription and the appended claims. r

In the description of my invention hereinafter set forth reference ishad to the accompanying drawing, of which: I

Figure 1 is a front elevational view of an upright electronic piano inwhich my invention is. embodied, the front portion of the. casing andthe keys, action, conventional pedals etc. as well as many of thestrings and pick-up electrodes being omitted for the sake of betterillustration, and certain of the electrical components being purelyschematically shown;

Figure 2 is a vertical cross-sectional view taken along the line 2-2 ofFigure 1;

Figure 3 is a vertical cross-sectional view taken along the line I3 ofFigure 1: Figure 4 is a substantially horizontal crosssectionalviewtaken along the line 4-4 of Figure 1; 39

Figure 5 is a view generally similar to Figure 4 but illustratingcertain modifications of my invention: and

Figure 6 is a vertical cross-sectional view takenalong the line 6-4 ofFigure 5.

Reference being had to Figures 1 through 4, there will be seen avertical metallic plate or frame I having upper portion 2 and lowerportion 3, and vertical side portions 4 and intermediate verticalreinforcing bars 5 Joining the up- 40 per and lower portions. Aforwardly extending flange 6 may be provided aroundthe periphery of theframe to facilitate its attachment to a casing for the instrument, whichcasing is indicated as 1. Thelower frame portion 3 may be progressivelyupwardly widened in its central and righthand portions, and in its lowerrlghthand corner it may be provided with a triangular aperture' Io.Along the bottom edge of the upper frame portion 2 and along the topedge of the lower frame portion 3 may be provided the respectiveforwardly extending ledges 8 and 8.

Strings I I, all for example substantially parallef-and verticallydisposed, are strung from hitch pins ll in the lower frame portion 3across 66 its ledge 9, up to and across ledge 8 and to conventionaltuning pins not herein necessary to show. Either one or more than onestring may be employed for each note of the instrument, there havingbeen illustrated by way of example one string for each of the bass(lefthand) notes and two strings for each of the treble (central andrighthand) notes. The string or strings for each note are adapted to bestruck a little below the ledge 8 by a respective hammer, as indicatedby the hammer 12 in Figures 2 and 3, and (excepting permissibly for thevery most treble notes) to be damped by a respective damper, as indi--cated by the damper l3 in Figure 3; the hammers and dampers may becontrolled by a conventional piano action not herein necessary to show.Just above the ledge 9 the strings pass over and bear lightly on abridge 55, being secured thereto as by conventional bridge pins Hi; theactive portions of the strings lie between the bridge i5 and the ledge8, and the bridge thus forms a support for the strings at the lowerextremities of their active portions. The strings are of course tuned toprogressive. fundamental frequencies, extending for example over a rangeof approximately six or seven octaves.

In the embodiment of the invention illustrated in Figures 1 through 4the bridge i5 is secured to is desirably of somewhat compliant ratherthan rigid material, and it may further be advantageously characterizedby at least some internal damping; wood, such as spruce or maple, may bementioned as suitable material, though no unnecessary limi-tationthereto is intended. In genera], the support for the bridge provided bythe plate 16, or the support for the strings provided by that platetogether with the bridge, will be recognized as a cantilever support;and it will be understood that. by virtue of its compliance it is avibratile support, and so serves to couple the strings togethervibrationally.

The plate I 6 may be extended upwardly beyond the bridge 16 sufficientlyto serve as a support for one or more translating systems havingsensitive portions in spaced relation to, and responsive to thevibrations oi, the strings. While any type of translating system may beemployed,

I have particularly illustrated herein translating systems of theelectrostatic type, whose sensitive portions are in the form ofelectrodes adjacent the strings. In the figures one translating systemis shown as comprising a strip 20 of insulating material, such as aphenol-resin composi-tlon product, secured to and extending forwardlyfrom the plate l6 a little above the bridge IS; 'a respective electrode22 for the string or strings of each note, preferably in the form of ascrew having its head behind the respective string or strings andpassing through the strip 20 and through an oversize hole 22a in theplate I8; and a conductor 24 electrically interconnecting the severalelectrodes 22, for example behind the plate [6.

By virtue of its position, this translating sys-- tem is responsive tothe vibrationsof portions of the strings quite near their lowerextremities; additional translating systems responsive to the vibratlonsof more upward string portions may of course be provided to makeselectively available a variety of oscillation and tone harmonicstructures. Such an additional translating system may also if desired becarried by the plate l6 above the first translating system, to which itmay be similar; it has been shown as comprising the strip 2! ofinsulating material, the electrodes 23 passing therethrough, and theconductor 25 for the electrodes 23 seen at-the righthand end of thestrip 2| in Figure 1.

The sets of electrodes 22 and 23 of course form with the strings smallcapacities which are Varied by string vibration, and the capacityvariations are caused to produce corresponding electric oscillations bythe impression of a high voltage across each of the capacities through ahigh resistance. Thus the metallic frame 5, with which the strings makecontact, has been shown as electrically grounded (i. e., connected to areference potential); and the conductors 24 and 25 have been shownconnected to first extremities of respective high resistances 26 and 27,of which the second extremities are connected together and to groundthrough a relatively high voltage source S. If the source S be a D. C.source, simple vibration-representing oscillations will be producedacross the resistances 26 and 21; while if the source S be ahigh-frequency (super-audible) A. C. source, high-frequencyoscillations, representing string vibrations by modulationscorresponding to those vibrations, will be produced across theresistances. The oscillations across the resistances may be appliedthrough respective condensers 28 and 29 to separate input channels 30and 3| of an amplifier system A, the amplifier system being operated todemodulate as well as to amplify if the high-frequency course S beemployed. Electrostatic shielding may be sufficiently disposed about thesensitive portions of all the apparatus feeding into amplifier system A,in well understood manner; it has been partially indicated schematicallyin Figure 1 as H.

In the amplifier system A, amplitude and phase controls may be includedfor the separate input channels, to provide harmonic structure controlin the manner disclosed in U. S. Patent No. 1,906,607; and common outputchannel controls 34 and 35, for example for frequency characteristic andvolume control respectively, may also be included. The common outputchannel 36 of the amplifier system may be connected, as by conductors31, to a loudspeaker or other electroacoustic translating device 38. Byway of example this has been shown as an electro-dynamic loudspeaker,disposed within the frame aperture 3a above-mentioned, and secured tothe lower frame portion 3 and to the righthand side frame portion 4 asby brackets 39. A baflle for the loudspeaker has been shown in Figure 2as formed by a front member 40 of the instrument casing.

In the case of soundboards of acoustic pianos, the predominant naturalfrequency of vibration varies somewhat from point to point along thebridge-i. e., between the portions respectively most closely associatedwith the various fre quency strings. Although of restricted degree, thisvariation of predominant natural frequency is of the same direction asthat of the string frequencies-e. g., it is an upward variation towardthe righ-thand or treble extremity of the instrument. In order that thevibratory reactions between the strings and the cantilever stringstrings and the conventional soundboard, I may arrange the cantileverstring support to have a progressively increasing predominant naturalfrequency in a rightward (treble-ward) direction.

In Figures 1 through 4 I have illustrated two dimensional variationseither or both of which may be employed to effect the natural frequencyvariation abovementioned. One of these is the progressive increase inthe thickness of the plate I6, taken in a rightward direction, thisincrease best appearing in Figure 4. The other dimensional variation isa progressive decrease of the overhang of the cantilever string support(i. e., of the dimension from the rigid spacing strip 11 to the bridge);this appears in Figures 1, 2 and 3, wherein it will be seen that in thelefthand (bass) portion the plate ll overhangs the frame portion 3 for aconsiderable distance between the strip l1 and the bridge, and that thestrip I1 is shaped and mounted to progressively reduce this overhang,ultimately to a very small distance in the righthand (treble) portion.It will be understood that the degree of each of these variations, themathematical progression according to which .each is carried out, andthe range of the scale over which each extends, may be varied withinwide limits without departure from the broadaspect of a substantialprogressive variation of the predominant natural frequency of thesupport from point to point. It will also be understood that each of thedimensional variations abovementioned, as well as the combination of thetwo, constitutes a progressive variation of the compliance of thestring-supporting or -coupling system, downwardly toward the trebleextremity.

In the very top bass or bottom treble regions of good acoustic pianos(or in general in the neighborhood of 100 cycles) the predominantnatural frequencies of the soundboard, as I have observed them at pointsalong the bridge, appear .to be approximately similar to the fundamentalfrequencies of the respectively associated strings; this fact I believeto be significant in contributing to the emciency and pleasing tonalqualities obtained from those instruments in this scale region. But thisapproximate similarity appears to be limited to about a one-octaverange; and the entire range of variation of the natural fre- .quency ofthe soundboard is typically from about 100 to about 500 cycles, or onlya little more than two octaves. Accordingly for the very low basestrings the predominant natural frequencies of the most closelyassociated soundboard portions stay materially higher than thefundamental string frequencies, whereas for the higher treble stringsthe predominant natural frequencies of the soundboard stay materiallylower than the fundamental string frequencies. The mentioned conditionin the low bass I believe to be significant in contributing to the poorfundamental and lower partial development in the string vibration, sincebeneficial resonant reactions between string and soundboard occur atupper partials of the string vibration; and the mentioned condition inthe higher treble I believe to be significant in contributing to therelative smallness of string vibrational amplitude, since any resonanteffect is largely lost and a poor impedance match is established betweenstring and soundboard.

At least largely to cure these conditions I may extend the range ofvariation of predominant natural frequency of the string-supporting or I-coupling means upwardly well beyond 500 cycles and preferably wellbeyond 1,000 cycles (at the treble extremity) and downwardly well below100 cycles (at the bass extremity) so that the range is one of at leastthree and preferably of more octaves; thereby I may readily extend therange of approximate similarity, between that predominant naturalfrequency and frequency of the associated strings, to at least threeoctaves and in cases even further, obtaining over a very substantialportion of the whole scale the advantages conventionally obtained in avery restricted region only.

bridge from the spacing strip I], to establish compliances which, withthe effective mass values of the plate l6, bridge l5, translating systemportions 2!, 22, 23, 24 (when these are mounted on the plate l6 asshown), etc., will produce the desired predominant natural vibrationalfrequencies at the several points along the bridge. It may be mentionedthat since the presence of the strings in their normal positions andtensions influences the effective parameters of the system (as bycontinually applying a rearward force to plate l6, contributing at leastslightly to the effective total mass, etc.), observations of predominantnatural frequency at various points are desirably made with the stringsin place and under normal tensions.

It will be understood that the proper absolute values of the thicknessesand overhangs at various points will depend not only on the degree andextent of the desired variation of predominant natural frequency of thestring-coupling or -supporting means, but also on the characteristics ofthe material of which the plate I6 is made, the

effective masses abovementioned, etc.; these values are, however,readily determined by test for any given material and under any givenset v of other conditions.

and phase characteristics of the amplifying means until the bridge mostfreely executes sustained vibrations--of which the fundamental frequencymay be'taken as the predominant natural frequency of vibration at thepoint in question.

Over and above the advantages abovementioned, the closer similarity ofpredominant natural frequency of the string-supporting means and thefundamental string frequency in the higher treble region further tendsto reduce the relative prominence of the thud or rap componentscustomarily noticeable in the higher treble tones as an incident. oftone inception. This component is caused essentially by the transientvibration of the supporting means at the predominant natural frequencyof its portion most closely associated with the struck string, whichvibration is translated to a considerable extent by all the electrodesin this region. The raising of that natural frequency to approximate thestring'frequency tends to cause this component to be better obscured bythe pure tone component, both because of the frequency change in itself,and because of an amplitude decrease 75 of the first component and anamplitude increase of the second.

The cantilever support need not be in the form ofa continuous platesuchas It. It may alternatively, for example, be in the form of a pluralityof individual supporting members supporting the bridge i5 at frequentintervals along its length; this has been illustrated in Figures 5 and 6by the narrow individual supporting strips or members 19, each securedin its lower portion to the back of the frame portion 3 through thespacing strip ll of earlier figures and extending upwardly to havesecured thereto the bridge l5 and, if desired, sufficiently further tosupport one or more translating systems (e. g., strips 20 and 22). Itwill be understood that the supporting members i 9 serve essentially assprings; and they may be appropriately stiff metallic springs, althoughwood or other material with appreciable internal damping may besubstituted if desired. While their absolute values will be dependentamong other things on the material employed, the

thicknesses and overhangs of the several mem-,

bers l8 may be chosen in the manner of and for the results effected bythe progressive dimensioning of the plate It in the earlier embodiment.

Although the sound-radiating and -collecting surfaces of the vibratilesupport in the instruments above described are small, the closeproximity of the loudspeaker 38 may occasion some undesirable acousticfeed-back to the support and strings; moreover slight feed-back byvibration conduction to' the-support and strings may occur through theframe i of the instrument. To counteract or neutralize these feed-backsI have shown in both embodiments a plurality of electro-mechanicaitranslating devices mounted to vibrationally influence the support, andelectrically supplied with output oscillations from the amplifierappropriate to subject the support to a vibrating force substantiallyequal and opposite to the feed-back forces influencing the support.These electro-mechanicai translating devices may be of any desired form;by way of simple illustration I have shown them as polarized elec--tromagnets 43, positioned behind various portions of the plate It (inFigures 1 through 4) or behind various ones of the vibratile supportingmembers It (in Figures 5 and 6), preferably opposite bridge l5. They maybe substantially rigidly mounted, on relatively heavymetallic brackets42 terminally secured to frame portion 3 as by appropriate ones of thebolts I8, and their poles may be very slightly spaced from the backsurfaces of respective armatures ll secured against the back of plate I8and preferably eleo-' trically grounded, or from the back surfaces ofthe respective supporting members I! (in Figures 5 and 6) when thelatter are of magnetic material. They may be supplied with outputoscillations from the amplifying system A, preferably through adjustablefilter and phase-controlling networks 48 (serving to control phaseprogressively as well as in respect of reversal) autismplitude controls48; these may be individual to the several devices for the obtainment ofthe most accurate neutralizing effects. With a small numher, or evenone, of these devices with carefully regulated oscillation supplythereto, there may be neutralized very large feed-back forces from theloudspeaker l8-such for example as may occur to string-supportingsystems of as large areaas conventional soundboards and the like.

While I prefer to associate feed-back neutralizing devices with thevibratile string-supporting system, as described above for the device43, I may alternatively employ neutralizing devices in association withthe strings themselves. In, United States Patent No. 1,929,031 to me Idisclosed feed-back to the strings of a mechanicoelectro-acousticinstrument; but that feed-back was to all the strings, which latter wereuncoupled from each other. I have found that in a coupled-stringinstrument of the class herein described I may efiiciently suppressfeed-back arising through the coupling system by associating anelectro-mechanicai translating device with a restricted number ofstrings only, such as the strings-of a single note. This I haveillustrated .in Figures 1' and 4 by the electro-mechanicaltranslating-device 48 secured, just above and infiuencing the strings ofone note, on the bottom of a cross-member 49 between the frame members5; this may be connected, through a filter and phase-controlling network45 and amplitude control 46 as above described for devices 43, to theoutput of the amplifier system A. By proper se-, lection of the stringsinvolved and of the control adjustments, this structure may be made tosuppress quite troublesome feed-backs.

While I have disclosed my invention in terms of particular embodimentsthereof, I do not intend any unnecessary limitations by virtue of thedetails of those embodiments, which are illustrative rather thancomprehensive. The scope of my invention is expressed in the followingclaims, in many of which I undertake to express that scope broadly,subject however to such proper limitations as the state of the art mayimpose.

I claim:

1. In an electronic piano having a plurality of progressively tunedvibratable strings and mecha-nico-electro-acoustic means for translatingstring vibrations into sound: the combination of a frame comprisingaapair of support members between which said strings are strung; andstringcoupling means comprising a bridge disposed adjacent one of saidsupport members and engaged by said strings, and vibratile means havinga portion secured to said one support member, extending therefrom incantilever to support said bridge, and having at most a small extensionbeyond said bridge.

2. In an electronic piano having a plurality of progressively tunedvibratable strings and mechanico-electro-acoustic means for translatingstring vibrations into sound: the combination of a frame comprising apair of support members between which said strings are strung; andstring-coupling means comprising a bridge disposedadjacent one of saidsupport members and engaged, at progressive points therealong, by saidstrings. and vibratile means having a portion secured to said onesupport member, extending therefrom in cantilever to support saidbridge, and having at most a small extension beyond said bridge, saidstring-coupling means being characterized, at points along said bridgeassociated with progressively higher-frequency strings. by progressivelyhigher predominant natural frequencies of vibration.

3. In an electronic piano having a plurality. of progressively tunedvibratable strings and mechanico-electroacoustic means for translatingstring vibrations into sound: the combination of aframe comprising apair of support members between which said strings are strung; andstring; coupling means comprising a bridge disposed adjacent one of saidsupport members and engaged, at progressive points therealong, by saidstrings,

and vibratile means having a portion secured to said one support member,extending therefrom in cantilever to support said bridge, and having atmost a small extension beyond said bridge, a

the distance of said bridge from said secured portion progressivelydecreasing toward the extremity of said bridge with which thehigher-frequency strings are associated.

4. In an electronic piano having a plurality of progressively tunedvibratable strings and mechanico-electroacoustic means for translatingness of said cantilever-extending means progressively increasing .towardthe extremity of said bridge with which the higher-frequency strings areassociated. I I

5. In an electronic piano having a plurality of progressively tunedvibratable strings and mechanico-electro-acoustic means for translatingstring vibrations into sound: the combination of a frame in which saidstrings are strung; and string-coupling means comprising a bridgeengaged, at progressive points therealong, by said strings, andvibratile means having a portion secured to said frame and extendingtherefrom in cantilever to support said bridge, the distance of saidbridge from said secured portion progressively decreasing, and thethickness of said cantilever-extending means progressively increasing,toward the extremity of said bridge with which the higher-frequencystrings are associated.

6. In an electronic piano having a plurality ofprogressively tunedvibratable strings and mechanico-electro-a-coustic means for translatingstring vibrations into sound: the combination of a frame comprising apair of support members between which said strings are strung; andstring-coupling means comprising a bridge disposed adjacent one of saidsupport members and engaged, at progressive points therealong. by saidstrings, and vibratile means having a portion secured to said onesupport member, extending therefrom in cantileverto support saidbridge,- and having at most a small extension beyond said bridge, saidcantilever-extending means having a compliance progressively decreasingtoward the extremity of said bridge with which the higherfrequencystrings are associated.

7. In an electronic piano having mechanicaelectro-acoustic means fortranslating string vibrations into sound: the combination of a pluralityof progressively tuned strings: and stringcoupling means comprising abridge engaged, at progressive points therealong, by said strings, andvibratile means supporting said bridge, said string-coupling means beingcharacterized, at points along said bridge engaged by strings tuned tofundamental frequencies above 500 cycles, by predominant naturalfrequencies of vibration in excess of 500 cycles.

8. In an electronic piano having mechanicaelectm-acoustic means fortranslating string vibrations into sound: the combinationof a pluralityof progressively tuned strings; and stringcoupling means comprising abridge engaged, at

' progressive points therealong, by said strings, and

vibratile means supporting said bridge, said string-coupling means beingcharacterized, at points along said bridge engaged by strings tuned tofundamental frequencies above 1,000 cycles, by predominant naturalfrequencies of vibration in excess of 1,000 cycles.

9. In an electronic piano having mechanicoelectro-lacoustic means fortranslating string vibrations into sound: the combination of a pluralityof progressively tuned strings; and stringcoupling means comprising abridge engaged, at progressive points therealong, .by said, strings, andvibratile means supporting said bridge, said string-coupling means beingcharacterized, at points along said bridge engaged by strings tuned tofundamental frequencies below 100 cycles, by predominant naturalfrequencies of vibration below 100 cycles.

10. In an electronic piano having mechanicaelectro-acoustic means fortranslating string vibrations into sound: the combination of a pluralityof progressively tuned strings; and stringcoupling means comprising abridge engaged, at progressive points therealong, by said strings, andvibratile means supporting said bridge, said string-coupling means beingcharacterized, at points along said bridge engaged by strings tunedthroughout a fundamental frequency range of at least three octaves, bypredominant natural frequenciesof vibration approximating thefundamental frequencies of the strings respectively engaging those,points. 11. In an electronic piano having mechanicoelectro-acousticmeans for translating string vibrations into sound: the combination of aplurality of progressively tuned strings; and stringooupling meanscomprising abridge engaged, at

progressive points therealong, by said strings, and vibratile meanssupporting said bridge, said string-coupling means being characterized,at progressive points along said bridge, by predominant naturalfrequencies of vibration varying through at least a three-octave range.

12; In an electronic piano having a plurality of progressively tunedvibratable strings and mechanico-electro-acoustic means for translatingstring vibrations into sound: the combination of a frame in which saidstrings are strung; and string-coupling means comprising a bridgeengaged, at progressive polnts'therealong, by said strings, and aplurality of vibratile supports having portions secured to said frameand extending therefrom in cantilever to supportsaid bridge atprogressive points therealong, said vibratile supports being ofprogressive compliances.

, 13. In a musical instrument having a plurality of tuned vibrators andmechanico-electric means for translating their vibrations into electricoscillations and an amplifier for said oscillations: the combination ofvibratile means vibrationally coupled to all of said vibrators;electro-acoustic translating means'supplied with oscillations fromlations of phase and amplitude to produce a vibrational influence ofsaid apparatus on said vibratile means opposing said feed-backinfluence.

14. In a musical instrument having a plurality of tuned vibrators andmechanico-electric'means for translating their vibrations into electricoscillations and an amplifier for said oscillations: the combination ofvibratile means vibrationally coupled to all of said vibrators;electro-acoustic translating means supplied with oscillations from saidamplifier and having a vibrational feedback influence on said vibratilemeans and vibrators; and feed-back opposing means, comprising aplurality oi! electro-mechanical translating devices variouslyassociated with said vibratile means, and means connected between saidamplifier and said devices for supplying to said devices oscillations ofphase and amplitude to produce a vibrational influence of said deviceson said vi bratile means opposing said feed-back influence. 15. In amusical instrument having a plurality of tuned vibrators andmechanico-electric means for translating their vibrations into electricoscillations and an amplifier for said oscillations: the combination ofvibratile means vibrationally coupled .to all of said vibrators;electro-acoustic translating means supplied with oscillations from saidamplifier and having a vibrational feed-back influence on said vibratilemeans and vibrators; and feed-back opposing means, comprisingelectro-mechanical translating apparatus immediately associated-withsaid vibratile means, means for supplying oscillations from saidamplifier to said apparatus, and means included in said supplying meansfor controlling the phase and amplitude of said last-mentionedoscillations.

'16. In a musical instrument having a plurality 1o! tuned vibrators andmechanico-electric 1 means for translating their vibrations intoelectric oscillations and an amplifier for said oscillations: thecombination of vibratile means vibrationally coupled to all of saidvibrators; electro-acoustic translating means supplied withoscillat-ions from said amplifier and having a .vibrational Ieed-baclginfluence on said vibratile means and vibrators; and feed-back opposingmeans, comprising a plurality of electro-mechanical translating devicesvariously associated with said vibratile means, means for supplyingoscillations from said amplifier to each .of said devices, andindividual means included in said supplying means for controlling thephase and amplitude of the oscillations supplied to each device.

1'7. In a musical instrument having a plurality of progressively tunedvibrators and mechanico-electric means for translating their vibrationsinto electric oscillations and an amplifier for said oscillations: thecombination of vibratile means vibrationally coupled to all of saidvibrators; electro-acoustic translating means supplied with oscillationsfrom said amplifier and having a vibrational feed-back influence on saidvibratile means and vibrators; and feed-back opposing means, comprisingelectro-mechanical translating apparatus immediately associated with arestricted number only of said vibrators, means for supplyingoscillations from said amplifier to said apparatus, and means includedin said supplying means for controlling .the phase and amplitude of thoscillations supplied to said apparatus.

BENJAMIN F. MIESSNER.

